Carrier-wave signaling system



A 927 H. MvPRUDEN CARRi ER wAvr; SIGN LING SYSTEM Filed Mljfi 25. 1925' DETECTOR I OSCILLATOR MODULATOR 6% m I amr JV Pokmzedl YWa/v/aMP/z/den by my,

Patented Apr. 12, 1927.

UNITED STATES PATENT, OFFICE.

HAROLD M. PRUDEN, OF WYOMING, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. 'Y.,

A CQgRPORATION OF NEW YORK.

CARRI R-WAVE SIGNALING SYSTEM.

Application filed March 25, 1925. Serial No. 18,125.

This invention relates to carrier wave sig-,

naling systems and particularly to ringing circuits therefor.

An object of the invention is to simplify the tlitDSll'llSSiOl'l of ringing signals in carrier wave signaling systems,

A related object ofthe invention is to transmit a ringing signal by means of a new and improved arrangement for changing the frequency of the carrier wave.

' Another object of the invention is to economize in the apparatus employed in systems ofthis type:

The invention is particularly applicable to carrier .wave signaling systems in which the carrier is suppressed at the transmitting terminal, and a side band alone is trans- ..mitted.

In systems of this type, difliculty has been for the reason that the terminal filters are usually so designed as to cause a high attenuation to the unmodulatedcarrier frequency component, and hence will also impose a very high transmission loss upon frequencies near the carrier frequency. It is therefore very diflicult to transmit a side .band obtained by modulating the carrier current in accordance with the usual ringing current of 20 cycles or 135 cycles. Y

This difliculty is overcome in the present invention which provides a ringing circuit for carrier suppression systems in which a 20 cycle ringing current is utilized to convert mitting channel into an oscillator and amplifier atlaptcd to generate and amplify a carrier wave of a frequency which lies within the transn'iission range of the terminal band filter.

The carrier wave of changed'frequency is mechanically modulated by interrupting the output of the converted circuit at the rate of The drawin shows the necessar circuits encountered in transmitting ringing signalsa balanced oscillator-modulator in the trans.

which would enable one to conduct/a complete two-way conversation from low ,frequency line L over the carrier line ML to a distant station and to transmit and receive ringing signals over the carrier line.

The low frequency line L may be an ordinary subscribers telephone'circuit; A radiating conductor may, of course, be employed in place of the carrier line ML when it is desired to apply the invention to radio systems. l y The low frequency line L is associated with the transmitting channel TL and the receiving channel R-L of the carrier system through the usual hybrid coil H and associated balancing network N. v

The transmitting channel TL includes a balance oscillator-modulator OM and a transmitting band filter TF. The receiving channel .RL includes a receiving band filter RF, a balanced detector D and alow-pass filter LPF.

The carrier currents which are utilized for transmitting and receiving signals over'the frequencies to the receiving channel RL. The filters TF and RF serve toseparate the respective bands of frequencies'ito the transmitting and receiving channels. These filters, as well as the low-pass filter LPF, may be desi gned 'in accordance with the principles set forth in the U. S. patent to Campbell, No. 1,227,113, issued May 22, 1917.

Oscillator-modulator and detector.

The oscillator-modulator OM and detector I) may be of any suitable type, such as that disclosed and claimed in a copending application of H. S. Black, Serial No. 58,744 filed September 26, 1925, consisting of balanced self-oscillating circuits adapted to suppress .the carrier.

to the primary windingof output transformer '3.

The detector D comprises a pair of threeg; l Lt,

elcnnirnt electron discharge tubes d and l haviiui their innit circuits connected to the secondary winding of input transformer t),

he oscillator-modulator from a battery ti, through choice coil 9, and the pri mary winding of transformer o. the bat tcry as also supplies space current to tubes and oi the detector through choke coil. 10 and the primary winding of transformer 7. The condanscr 11 serves to reduce the common impedance of the space current supply circuit to a minimum in order to prevent reaction between the oscillatorn1odulato and detector circuits.

'lhe oscillator-modulator and detector circuits are generally similar in construo tion, and hence only the elements oi the oscillator-modulator will be described in do tail. r

.The tubes 1 and 2 oscillate in pa 'allcl at the carrier irerp1e1'icy,'the grid voltages on each tube rising and falling in synchronismi The frequency control consists of an oscillating element including an oscillating coil 12 and a variable condenser 13, coupled to the anodes of tubes 1 and by means ot a feedback resistance 1st and th primary windings of output transformer 13. p

it biasing resistance 15 is shunted across the feed-back resistance It and the oscillating element 152, 13 in order to maintain the external impedance oi the output circuits low to the carrier frequency, thereby increasing the load'carrying capacity, stability and output level. The blocking conden scr l5 serves to prevent the source of space current 8 from bein short-circuited. 'lhe blocking condenser 17 provides a low impedance path to the oscillating currents and also prevents the battery 8 from being shortcircuited when the oscillator-modulatoris converted for ringing purposes, as herein after described.

Grid resistances 18 and 19 areiemployed for the purpose of increasing the stability of the oscillator-modulator, and tor the purpose of eliminating the auxiliary batteries which are usually employed to apply the required negative bias to the grids of the tubes. When the tubes 1 and 2 oscillate in parallel, the grids draw current during the The resistances 18 and 1 9'are very large.

and the circuit is so adjusted that any involtage re tor input circuits high to the impressed.

"voice frequency ciu'rents. lly regulating the value of this resistance the cllcct ot the lance trequcncy currents winch in practice are found to ,bepresent in this part oi? the circuit, may be rendered negligible. llesistance elements 12.3 and ill; may be c1n- 'ployed to stabilize the input impedance oi:

the oscillator-modulainc Transmitting telephone signals.

'lhc oscillator nn\dulator UM norn'lally geueratcsa carrier wave which is utilized for communication purposca l 01cc currents originating in the low frequency line L are combined with the carrier wave in the oscillatorqnodulator, the carrier being suppressed in the usual. manner. (inc ol the side bands produced by modulation, for ex.- amplc, the lower side band, is transmitted through the filter Tl? to the carrier line ML,

While the other side band, :lfor example the upper side band is suppresaerl by the filter 'lli. Y

' elimiiarly, the detector 1) gene ates a carrier Wave which is utilized in the reception of telephonic signals. Voice modu lated waves incoming over the line hell) are picked up by the baud tiller RF and are demodulated in the detector 1). The voice frequency components of demodulation are transmitted through transformer 7, low pass lilter LPF and hybrid coil ill to the low frequenoy line L. High frequency components appearing in the output of the detector are suppressed by the low pass lilter LPF.

A Ringing.

in transmitting ringing signals over the carrier line ML, it "will be evident that it th carrier wave normally generated by the oscillatoranodulatdr OM were directly modulated by a EEO-cycle ringing current, the rcsulting side band would not be eliicicntly transmitted by the filter TI That is, the lilter Tia, Whichis designed to greatly attenuate the carrier frequency of" say 7000 cycles would impose too great a loss upon the 6980- cycle side band.

In accordance with the invention, ringing signals are transmitted over the line ML by a, in the grid till converting the balanced oscillator-m0dulator OM into an oscillator and amplifier adapted to generate and amplify a carrier Wave of a frequency which lies within the transmission 'angcof the band lilter TF. The wave of changed frequency is then intermittently interrupted at the, ate of cycles -per second and impressed upon the line .ML.

The operation of the system for transmitting ringing signals is as follows: Y

- The ,20-cycle ringing current incoming over the low frequency li'neyIJ is impressed over the back contacts ofrelay upon an alternating current relay 20 and a polarized relay short-circuits the receiving channel RL to prevent incoming signals from being transmitted to the line L during the transmission ofr-inging signals, and at contact 31 short-circuits the hybrid coilH to prevent the 20 cycle ringing cur-- went from being transmitted to the channel TL. Relay 28 also closes contacts and 3. At contact this relay closes one branch of a short-circuit across the secondary winding of output transformer 3, so that the output of thetransmitting channel TL is intermittently interruptedatthe rate of 20 cycles per second by the alternate energizetion and deeuergization of the polarized relay 27. 7

Relay 29 at its-left hand contagt opens the plate circuit of thetube 2, thereby unbalanciug the oscillator-niodulator OM, an d.eouuects condenser 34 in the plate circuit of the tube 2. The oscillator-modulator OM is thus converted into an oscillator tube 2 and an amplifier tube 1- eonnected, in tandem. Space current is supplied to the amplifier tube 1 in the same manner as before. Spacecurrent, however. is supplied to the oscillator tube 2 from thebattery 8. through contact 32 of relay 28. primary windingof oscillating coil 12 and armature and left hand contact of relay 29.

\Vhen the circuit is converted in the manner described above, the secondary winding of the oscillating coil'12 is in the grid circuits of both the amplifier tube 1 and the oscillator tube2; Hence, the output of the oscillator tube 2 which is fed back to its grid eircuit is impressed upon the grid circuit of the amplifier tube 1. By including the condenser 3% in the oscillating circuit of the tube 2, the oscillator will generate a carrier wave of a predeterminedfrequeneytfor example 5000 cycles, which lies within the transmission range of the band filter Th. The biasing resistance 15.is short-circuitefl at the right-hand contact of relay 2.) and hence the output circuit of the amplifier tube 1 may be traced from the anode, through primary winding of ransformcr 3, armature and right hand contact of relayBE), condenser 1.6, to the cathode of tube 1. The car rier currents generated by the-oscillator tube 2,-which are amplified in the tube 1, are thus transmitted through the transformer 3. The output of transmitting channel TL, as pointed out above, is intermittently short circuited at. the rate of 20 cycles per second, so that a carrier wave interrupted at 20 cycles per second, lying well within the transmission range of the filter TF, is impressed upon the high frequency line ML. The receiving operation is as follows:

The carrier wave interrupted at theLrate of 20 cycles per second incoming over the line ML 'will 'lie within the transmission 1 these even order modulation products in eluding a -20-eycle wave component." The 20-cycle ringing current derived from the common outp-ut path of the balanced'detector D is impressed upon the relay 36. which I is tuned to 20.,eycles. The choke coil 10 offers a high impedance to currents of 20 :eycles and hence none of the ringing carrent will be dissipated in the common space current supply circuit.

Relay 30 at'its front contact energized re-.

lay 37 over a circuit extending-from ground. through battery 38, windingof relay .37, armature and front contact of relay 36, baclt contact and armature of alternating current relay 26, to ground. Hence, ifthe back contact of relay 26 is open, as it is during the period when the oscillator-modulator OM is converted for the transmission of ringing signals, the relay 37 cannot be energized. Therelay 37 is slow acting and is adapted -to remain operated only when the relay is intermittently opcrated'at the rate of cycles per second, and hence the relay -will not remain operated in response to voice currents or other irregular impulses incoming over the line. i

' The 0 ration of relay 37,-in the manner describe which is normally energized over an obvious circuit. Relay 39 is a slow releasing relay and is adapted to close its front contact to actuate relay 25 only when relay 37 remains operated for a predetermined period. Relay 25 in operating connects its armatures to a iii above, short-circuits relay 39" l proposes in which case the ringing:

lll

ringing: source of fill cycles, thus transitlilting. riu inp; current over the low :lreipaency line. i...

ll will lie understotul, oli course, that the terminal circuits ma he arranged to transwit the upper side hand for connuuniealion and would he trzulsmittedliy increasing the [reanchor at the carrier wave in any suitable manner. a i

The invention is. of course, susceptible of various other modifications and adaptations not specifically referred to but included within thescopo oi the appended clain'is.

lVhat is claimed is: i

l. in a, signaling system, a carrier channel including a source of carrier waves, means in said chalnicl for suppressing a range of tie qucnciee including; the carrier and for lreely transmitting another range of frequencies, means for shifting; the frequency oi the mvcs from said source to a point within said last mentioned range o'l: frequencies, and means :tor intermittently interrupting the wares oi changed :trequenc r.

it. In a. signaling, system, a

transiuitl ing channel including a source oi carrier waves,

(w ad u tit) a wave lilter for suppressing the carrier and the frequencies lying" to one side thereof and for :treel transmitting waves of 'l'rclpiencies lying); to the other side or the carrier, means for shitting the frequency ot the ares gen erated by said source to a point within the free transmission range of said filter, and means for intermittently interrupting the waves of changed frequency.

3. In a signaling system, a carrier channel connecting a low frequency circuit and a carrier circuit, a source of carrier waves in said channel, a wave filter connected hetween said source and said carrier circuit and adapted to suppress a range of frequencies including the carrier and to freely trans init another range of frequencies, and means associated with said low frequency circuit to slutt the frequency of the waves from S2l1(l' sourceto a point. within the free transn1isrion range of said filter and to intermittently short-circuit said filter.

4. In a signaling: system, a balanced oscillzlitll'dlltnltlltltt)! adapted to generate carrier waves il or signaling purposes, and means to convert said oscillatoraimdiilator into an oseillator and an'iplitier adapted to supply waves of afrequency dill'erent from that of the carrier. 7

5. In a signaling system, a transmission line, a balanced hscillator-modulator 51sec ciated therewith and adapted to generate carrier waves for signaling purposes, means to convert said l1seillator-luodulator into an oscillator and amplifier adapted to supply l, a t l til wart-s at: a. trcquency dillcrcnt from that at the carrier, and means tor lnoiilulating said waves of dillcrent fireauen'cy in accordance with a ringing signal.

(1. ln a signaling system, a carrier channel including a balanced oscilla.or-niodnlator adapted to e'tuieratecarrier waves and upon which signaling waves may he iu'iprcssed lneansin said channel for alip firessing a range of frequencies including the carrier and tor freely transmitting another range ot frequencies, and ll'ltffll'lSlO convert said oscillatoranodulator into an oscillator and amplifier adapted to generate and amplify uaveslying within said lastmentioned rangeof frequencies. I

'1 In a signaling system, a carrier channel including a balanced oscillatoranodulator adapted to generate carrier i avcs, means to impress signaling waves upon said-oscillator-modalator, means in said channel for suppressing a range of frequencies including the carrier and-for freely transmitting are ill) t). In a signaling system, a carrier chan- 1101 having a source ol carrier waves and means for modulating the carrier waves in accordance with voice currents, means for changing the frequency of the waves from said source, and means for intermittently interrupting the waves ofchanged 'l're qucncy.

10,. In a signaling system, a carrier channel having two thermionic tubcs serving as a. iJtiltlIlCGCl oscillator-i'nodulator to generate carrier waves upon whichfsignal waves. may be impressed, means in said channel for suppressing 'a range of frequencies including the carrier and l'orlrcely transmitting anotherrange of frequencies, and means to convert'said tubes into an oscillator and amplifier to generate and amplify waves lying within said last-mentioned range of frequencies. In witness whereof, I hereunto subscribe my name this 12 day oi. March, A. D. 1925.

HAROLD M. PRUDEN,

no I 

